Study On The Polypropylene Composite Filled With Surface Modification Of Needle-like Wollastonite

Polypropylene(PP) is an excellent thermoplastic, which has a number of properties and so it is widely used in a plenty of applicantion. However, its low mechnical strength, large molding shrinkage rate, low modulus and poor impact resistance limit its further application. In order to improve its strength, modulus and the impact resistance, we need to treat PP through the reasonable enhanced modification.According to the unique needle characteristics of wollastonite, on this issue, by means of four different surface treatment technologies (eg.:coupling agent treatment, cellulose treatment, SiO2 coating treatment and Si02/coupling agent and SiO2/NCC co-processing treat wollastonite) the wollastonite was treated separately, and the composites of polypropylene(PP) filled with needle-like wollastonite after treatment were prepared by melting blending through extruder. The treatment needle-like wollastonite effect was evaluated by infrared spectroscopy(FTIR), scanning electron microscopy(SEM) respectively. Meanwhile, the mechanical properties of PP/wollastonite composites were studied via mechanical testing machines and hardness measuring instrument, the rheological behavior were studied via dynamic rheometer. Differential scanning calorimetry (DSC), polarizing microscope (POM) were applied to analyze the crystallization properties of the composites. Thermo-gravimetric analyzer (TGA) was applied to test the changes on thermal stability of the material. In addition, use of scanning electron microscopy(SEM) to observe the fracture surface of composites. In the paper, discussed the effect on structure and properties of PP/wollastonite composites of different surface treatment technologies and different dosage.The data showed that:(1) The FTIR results showed that there were chemical reaction between the wollastonite with four kind of coupling agents, and the activation index value showed there was better effect of coupling agent KH570 and DL-411-A on the surface modification for wollastonite. When the mass ratio of KH570 and DL-411-A was 2.0wt% and 1.5wt% of wollastonite respectively, the tensile strength and flexural strength of PP/wollastonite composites reached a maximum value. The melt flowability of the composites was significantly improved by the addition of DL-411-A coupling agent. At the same time, there were better dispersion and interface compatibility of wollastonite with the matrix PP.(2) Introduction of MCC, NCC maked wollastonite particles surface hydroxyl groups and the specific surface area increased, to some extent, could improve the rigidity and hardness of the composite system. The interface combination of wollastonite and PP matrix and the impact toughness were enhanced by surface treatment. It improved thermal stability, enhanced the viscosity of compsites, and PP/wollastonite composites still are the pseudoplastic fluid.(3) After wollastonite was coated by SiO2, the particle surface became rough, the edges were passivated and the surface properties were improved. Along with the content of SiO2 increased, the crystallinity decreased, the crystallization rate increased and the spherulite size decreased. SiO2 particles play the role of heterogeneous nucleation, which resulted in recrystallization peak appeared during the composites melting. It strengthened the toughness and heat resistance, improved thermal stability of the composite system.(4) Compared with single treatment, the surface of wollastonite hydroxyl groups and roughness increased significantly by co-processing treatment. The best effect were SiO2/KH570 and SiO2/NCC treatment, in this moment, the properties of tensile, flexural, impact and the melt fluidity greatly increased, and the treatment of wollastonite has played a very good effect in the aspect of toughening and reinforcing. At the same time, in the crystallization process, the spherulite size reduced, nucleation number increased, the interface combination enhanced and there were better interface compatibility of wollastonite with the matrix PP. The co-processing treatment could significantly delay thermal decomposition of PP/wollastonite composites.(5) With the content of wollastonite increased, however, the rigidity and toughness of PP/wollastonite composites decreased significantly. It had little impact on processing fluidity of PP/wollastonite composites. Meanwhile, there were poor dispersion and interface compatibility of wollastonite with the matrix PP. When the wollastonite content of 20wt%, the composite system had the best overall comprehensive performance.